1. Field of the Invention
The invention relates to a multipart cooled piston for a combustion engine with a piston upper part of forged steel, comprising a combustion bowl in the piston crown and a ring wall with ring belt, and with a piston lower part comprising a piston skirt, pin bosses for receiving the piston pin connecting the piston to the connecting rod, and pin boss supports connected to the piston skirt. A cooling channel is formed by both the piston upper part and the piston lower part and is limited in its cross-section by these.
2. The Prior Art
A multipart cooled piston for a combustion engine is known from Japanese Patent No. JP 61175255 A. This piston has at the level of the ring belt of the piston a number of ribs, between which is arranged a thermally insulating plate for minimization of the heat transfer from the combustion chamber bowl to the ring belt.
From WO 00/77379 A1, a further piston for a combustion engine is known which has a wall section with several transverse walls made of thin metal sheet which are radially arranged in order to improve the heat dissipation in the cooling channel.
The above designs are not suitable for improvement of the piston with respect to its stability for high ignition pressures and temperatures as encountered in modern diesel engines.
It is therefore an object of the present invention to provide a multipart cooled piston which can be manufactured inexpensively with a sufficient form stability and with a cooling system with improved cooling effect.
This object is achieved by a piston having a cooling channel formed in the piston upper part which has holes spread over its circumference towards the piston crown, with the piston material present between such holes forming supporting ribs that each form sections of an all-round annular rib radially to the longitudinal piston axis. A piston lower part has an annular and all-round carrier rib connected to the pin boss supports. The piston upper part and the piston lower part are non-detachably connected to one another by the ring rib and the carrier rib, where the ring wall limiting the cooling channel forms by its wall cross-section a gap with the piston lower part, inside which a sealing element can be disposed.
With a piston manufactured in this way, the cooling channel can be formed closer towards the piston crown or combustion bowl and nevertheless has excellent form stability. In addition, the arrangement of the supporting ribs effects a kind of chamber formation inside the cooling channel, i.e. creates shaker areas, whereby a prolongation of the dwell time of the cooling oil is achieved and hence an improved heat dissipation of the piston areas to be cooled.